The very high speed (THD) connection or “backhaul” of the fourth generation of mobile radio (LTE), of Wifi terminals or Wifi points better known by the name “hot spots”, or else enterprises, consists in having a point-to-multipoint wireless network from a central station to terminals by setting up simultaneous links of very high speed, around 100 Mbps, from this central station or transmission hub to each terminal.
The coverage is often provided by sectors, typically of 90°. The capacity needs for the backhaul of the fourth generation of mobile radio are several gigabits per sector and more precisely a few Gigabits per km2. In order to attain such capacities, it is necessary to have very wide radio bands such as those available in digital wavelength microwave frequencies, or EHF for “Extremely High Frequency”, the only ones to have very wide bands greater than one GHZ (bands Q, W, E or D), or at centimeter wavelength microwave frequencies, or SHF for specially high frequency (bands Ku and Ka). For the case of SHF, the congested spectrum does not allow the required band to be obtained in the ether; on the other hand, at intermediate frequency (latent), the cost effectiveness of processing in this frequency range is at an optimum. There is little point/multipoint system of high capacity at present, and the local multipoint distribution service or LMDS from the Cambridge Telecom company and the FTTA system from the applicant, which is capable of multiplexing twenty or so modulators/demodulators or modems at 100 Mbps on a sector, may be cited.
Although the various systems operate correctly, it is necessary to increase the performance thereof, to optimize the spectral resources, the reuse of frequencies, for example, and to process capacity management (“load balancing”) or resilience problems.
The following definitions will be used in the description of the invention that follows.
The very high speed or THD relates to transmission speeds on each link of at least 20 Mbps, the high speed relating to speeds of 2 Mbps and above. The capacity is the total of the speeds on each link.
“Point-to-multipoint” systems use sector antennas at their central station, which set up the connections to the terminals situated under the coverage of the sector antenna. The transformation of a sector beam into a group of more directional beams with higher gains within this sector beam is denoted by the term “multibeam”. This is radiation from the central station to a sector that has a plurality of communication beams with a high gain greater than that of a sector antenna. The device for forming pathways associated with these beams is called an MBF for “multibeam former”. These pathways convey the multiplexes in the subsectors (beams) suited to the distribution of the terminals and to the speed requirements thereof. Each of the input ports of the MBF is provisioned by a multiplex from a plurality of modems, and there are as many multiplexers as subsectors or beams. The output ports of the MBF are each connected to an elementary antenna, directly if the pathways are formed at radiofrequency RF, or indirectly if the pathways are formed at intermediate frequency FI. The document WO 2008/049191 poses and solves the problem of minimization of the possible interference generated by electronic components.
The multiplex is the association of a plurality of waveforms sent on each of the beams, each waveform being transmitted on a channel that corresponds to a modem. Each of the beams can convey one or more bidirectional channels. A multiplex contains a plurality of channels, one channel is associated with a modem, and each of the channels has a different frequency and may have a different band and also a different modulation order. The multiplexes may be different from one another. There is thus a diversified capacity in a beam, said capacity being composed of diversified speeds.
The term “beam” denotes the radio lobes propagated in the ether. “Pathways” denote the paths followed in the circuits which, by microwave combination in the antenna system, will create the beams.
One of the aims of the present invention is to propose a system of very high capacity that is capable of delivering capacities of n*100 Mbps, where n is adjustable from the request, in a plurality of simultaneous directions in order to provide notably the following functions: a notable increase in the status of the links, optimization of the link statuses according to the distance at which a terminal is situated, better known by the expression “near-far”, a function of balancing of the streams known by the term “load balancing”, a resilience function, entry management for new terminals, and finally the rejection of interference from a sector with the neighbouring sector.